An implantable cardiac stimulus device (ICSD) is implanted into a patient in order to monitor and, if necessary, supplement or correct the electrical activity of the patient's heart. An ICSD may be configured to deliver pacing pulses to assist in regularizing heart function on an ongoing basis. An ICSD may also be configured to deliver defibrillation and/or cardioversion stimuli, which will typically be more energetic than pacing pulses. Some ICSDs can perform each of these functions in response to predetermined conditions.
With respect to the more energetic defibrillation and/or cardioversion stimuli, one goal of applying the stimulus is to change the state of heart function. For example, a tachyarrhythmia or fibrillation may be identified as malignant and can indicate therapy. One or more stimuli may be applied to convert the patient to normal sinus rhythm and/or a non-malignant rhythm. Some characteristics of the post-shock cardiac signal following successful conversion, for example, rate and morphology, may be quite different from those that occur prior to stimulus delivery. If conversion is not successful, however, the post-shock signal may have similar rate and morphology to the pre-shock signal. New and alternative methods and systems providing accurate detection of cardiac events following stimulus are desired.